It is known that internal combustion engines are equipped with so-called standard fuel injectors to inject metered quantities of fuel into the cylinders of the engine. Each standard fuel injector performs according to a standard characteristic curve that represents a correlation between an energizing time during which the standard fuel injector is energized and a fuel quantity injected by the standard fuel injector into a cylinder of the internal combustion engine. Due to the production spread and tolerances, the standard characteristic curve of each standard fuel injector is generally different from the others.
In order to guarantee substantially the same performances, it is therefore necessary to properly correct the standard characteristic curve of each individual standard fuel injector. A known strategy to achieve this task provides for testing a so called master fuel injector at the end of the production line, in order to determine a master characteristic curve of the master injector, and then of correcting the standard characteristic curve of each individual standard fuel injector with a correction factor derived from the main characteristic curve. This correction factor may be expressed in terms of a fuel quantity correction or in terms of an energizing time correction.
However, these correction strategies are based on the assumption that the standard characteristic curves have the same slope of the master characteristic curve. Therefore only in this special case, the effectiveness of the known correction strategies is actually guaranteed.